Method and apparatus for controlling x-ray intensity



M. MORRISON Sept. 4, 1934.

METHOD AND APPARATUS FOR CONTROLLING X-RAY INTENSITY Filed NOV. 20. 1931,MW/N Las? INVENTQR Mon/TF0@ MWF/,60N hf L ATTORNE JIL/IA v 70 4 m @2 Wl m @MAA w Z M Hmw n [[[III Auf J U amm u 1 mmmw rn nunmjf .v /MUPatented Sept. 4, 1934 METHOD AND APPARATUS FOR CONTROL- LING X-RAYINTENSITY AppllcatlonNovember 20, 1931, Serial No. 576,238

12 Claims. (Cl. Z50-34) UNITED STATESv PATENT' OFFICE,

My invention relates to X-ray apparatus and has particular relation toan X-ray apparatus wherein the intensity of the X-rays generated oremitted by the X-ray tube are automatically varied during energizationthereof.

More particularly stated my invention comprises the combination of anX-ray tube of the incandescent cathode type with an incandescent cathoderectier both of which are connected in 19 series with a suitable sourceof alternating current, and coordinated switching means are providedwhich through the operation of a time switch control the main operatingcurrent and the cathode heating current of the rectifier tube.

l5 The energy passing through the rectifier tube,

and consequently through the X-ray tube, is dependent upon thetemperature of the thermionic cathode of the rectifier tube and byvarying the energy supplied thereto, during predetermined periods oftime as controlled by the time switch, the intensity of the X-raysemanating from the X-ray tube during the period of energization thereofwill vary in accordance with these variations in cathode heatingtemperature.

This feature of producing X-rays of varying intensity is particularlyuseful in the taking of radiographic exposures as it results in apicture in which there is an entire absence of the socalled grid marksand the film appears to have a uniform density over its entire area.

The novel features of my invention will become readily apparent to thoseskilled in the art by reference to the accompanying drawing wherein`Figure 1 is a diagrammatical representation of an X-ray system inaccordance with my invention in which X-rays of varying intensity aregenerated.

Figure 2 is a graphic representation of the variance in the voltage ofthe rectier tube and the variance in the intensity of the X-raysemanating from the tube during a predetermined interval of time.

' Referring now to the drawing in detail I have shown a suitable sourceof alternating current of the usual commercial potential, such as agenerator 5. A high tension transformer 6 has one end of its secondarywinding 7 connected to the anode terminal of a vacuum valve or rectifiertube 8 by means of a conductor 9. The remaining end of the secondarywinding 7 is connected by means of a conductor 10 to the cathode end ofan X-ray tube 12 and the anode of this X-ray tube is connected to thecathode end of the rectifier tube through a conductor 13. y

A circuit is thus completed from the secondary winding 7 through theX-ray tube and rectifier tube enabling energy to flow therethroughduring each half wave of the alternating current cycle with theremaining half wave suppressed by the well known action of the rectifiertube 8. A 6" low tension transformer 14 has its secondary winding 15connected to the cathode of the X-ray tube 12 for the purpose ofsupplying heating currents to the same and the primary winding 16 isconnected, by means of a pair of conductors 17 55 and 18, to the sourceof supply' through a suitable switch 19.

The primary winding 20 of the high tension transformer 6 has one of itsends connected to the source of supply 5, by means of a conductor 22,while the remaining end thereof is connected to a contact terminal orbrush 23 though a conductor 24.

A similar contact terminal 25 is connected, by means of a conductor 26,to a junction 27 in 75 the conductor 17 so that when the switch 19 isclosed and the contact terminals 23 and 25 are bridged a circuit will beclosed to 'the primary winding 20 from the source 5 as can be readilyappreciated from the drawing.

A low tension transformer 28, similar to the transformer 14, has itssecondary winding 29 connected to the cathode of rectier tube 8 for thepurpose of supplying heating currents thereto. T'he primary winding 30of this transformer 85 has one of its ends connected to the source ofsupply 5, by means of a conductor 32, while the remaining end of thiswinding is connected to a contact terminal 33 by means of a conductor34. Another contact terminal 35 which is disposed 90 adjacent thislatter terminal 33 is connected to a resistance or rheostat 36 through aconductor 37.

'I'he remaining end of this rheostat is connected by means of aconductor 38 and the switch 19 to the source of supply 5. When,therefore, 95 the switch 19 is closed and the contact terminals 33 and35 are bridged a circuit will be completed to the primary winding 30.The cathode of the valve tube 8 will thus be heated to an electronemitting temperature allowing energy to flow in the main circuitcomprising the valve and X- ray tubes 8 and 9, respectively, and thesecondary winding '1.

In order to vary the energy supplied to the cathode of the valve tube 8and thereby regulate 105 the energy owing therethrough and through theX-ray tube, with an attendant variation in the intensity of the X-raysemanating from the latter,

I provide the resistance or rheostat 36 with a mQYable arm 39, to whicha flexible conductor 40 110 is attached in order to connect the arm withthe conductor 37 and contact terminal 35.

Movement, therefore, of this arm downwardly over the resistance 36decreases the total resistance or short circuits the same from thecathode heating circuit and accordingly increases the temperaturethereof. An increase of the cathode temperature enables a greaterpotential to flow through both valve and X-ray tubes with an increase inthe intensity of X-ray output due to a change in the wave length of theX-rays.

The arm 39 is insulated by means of a block 41 from other portionsthereof and is supported by means of a bearing portion 42 to the squarerod or shaft 43 upon which it is arranged to slide during its movement.This shaft 43 is in turn supported in a suitable manner, such as bybrackets 44 and 45, and a spring 46 surrounding the shaft 43 tends toretain the arm 39 in the upper extremity of its movement to allow only aminimum of heating energy to be supplied to the cathode of valve tube 8.

In order to actuate the movement of the arm 39 during the period ofenergization of the X-ray tube and to regulate the time period ofoperation of both, a timing mechanism of any well known type may beutilized. As this mechanism per se forms no part ofmy present inventiona detail description thereof is believed unnecessary. It is believedsuftlcient to state that when the mechanism is set for the time perioddesired a shaft 47, to which is secured an insulating member, such as adrum 48, is caused to move downwardly.

This insulating member 48 is provided with a pair of metallic surfaces49 and 50 of copper or other well known conducting material which duringmovement of the shaft 47 bridges the contact terminals 33, 35 and 23, 25respectively, thus completing the circuits to the primary windings 20and 30.

It must be noted that the metallic surface 50 is longer than that of thesurface 49 and the bridging of the contact terminals 23, 25 takes placetherefore before the remaining terminals 33, 35. This allows the primarywinding 20 to become energized a short period of time before the heatingof the cathode of the valve tube 8 and upon the latter reaching anelectron emitting temperature a discharge will follow and X-rays will begenerated by the X-ray tube 12.

Further downward movement of the shaft 47 and insulating member 48causes the same to contact the arm 39 and move the latter downwardly ofthe resistance 36 and square shaft 43 against the tension of`the spring46. This movement of the arm 39 short circuits the resistance 36 fromthe cathode heating circuit through the fiexible conductor 40 andenables the energy supplied to the cathode of the rectifier tube 8 toincrease. This in turn allows a greater amount of energy to flow throughthe rectifier tube and the series connected X-ray tube and results in anincrease in the intensity of the X-ray generated by the latter.

The movement of the shaft 47 and drum 48 being reciprocatory the arm 39will first completely short circuit the resistance 36 from the cathodeheating circuit and then as the shaft moves upwardly the resistance isagain cut into the circuit to again reduce the cathode heating energywith its attendant effect upon the main high tension circuit and theintensity of the X- rays generated. The period of time that therespective circuits are closed by the metallic surfaces 49 and 50 andthat required for one complete reciprocatory movement of the shaft 47and drum 48 is dependent upon the setting of the time switch which maybe adjusted as desired.

Regardless of whether this time setting be relatively small or large thetime switch will cause the complete operation of the associated parts asjust described, the only variance being in the rapidity with which thecycle of operation is performed.

Referring now more particularly to Figure 2 I have shown a graphicillustration of the variance in the voltage through the high tensioncircuit comprising the valve and X-ray tubes and the secondary winding 7caused by varying the heating energy supplied to the cathode of thevalve tube 8 in the manner just described. As the intensity of theX-'rays generated by the X-ray tube is dependent upon the voltageimpressed thereupon this ilgure is also representative of the variationin intensity of the X-rays.

It can be appreciated by reference to Figure 2 that at the time ofenergization of the X-ray tube and the closure of the circuit by themetallic bridging member 50 the intensity of the X-rays starts at thezero line and, as the resistance 36 is short circuited out of thecathode heating circuit by the movement of the arm 39 until the same iscompletely short circuited, the intensity of the X-rays reaches maximum.When the armA 36, therefore, completes its extremity of movement andstarts in the reverse direction through the action of the time switchthe resistance is again gradually inserted in the circuit until at theexpiration of the predetermined time period the intensity of the X-rayshas dropped from maximum to zero.

The rise and fall in peak voltage or intensity is, of course, gradualduring the movement of the arm 39 with periodic drop in voltage andintensity caused by the alternating current cycle which causes thevoltage and intensity to drop momentarily to the zero line. This canreadily be understood by reference to Figure 2 which is representativeof the gradual rise and fall of peak voltage and intensity over a periodof several alternating current cycles. Y

It thus becomes readily apparent to those skilled in the art that I haveprovided an X-ray system in which the intensity of the X-rays generatedby an X-ray tube is automatically varied during the predeterminedinterval of time of operation thereof regardless of the duration of thisperiod of energization. Furthermore, a uniform maximum intensity isalways obtained during the period of energization regardless of itsduration.

Although I have shown and described several embodiments of my inventionI do not desire to be limited thereto as various other modifications ofthe same may be made without departing from the spirit and scope of theappended claims:

What is claimed is:

1. The method of obtaining X-rays of varying intensity from an X-raytube which consists in supplying the X-ray tube with rectifiedvpulsating current, timing the period of energization of the X-ray tubeby the rectified pulsating current, and varying the maximum magnitude ofeach successive pulsation of the rectified pulsating current supplied tothe X-ray tube during the period of energization thereof to vary theintensity of the X-ray output of the tube during its operation.

2. The method of obtaining X-rays of varying intensity from an X-raytube energized from an alternating current source which consists inconverting the alternating current to rectified pulsating current andenergizing the X-ray tube therewith, timing the interval of energizationof the X-ray tube by the rectified pulsating current, and regulating theamount of rectified pulsating current supplied to the X-ray tube duringthe period of energization thereof to cause a variation in the magnitudeof each successive pulsation of the current with a correspondingvariation in the intensity of the X-rays emanating from the X-ray tube.

3. In an X-ray system for varying the AX-ray intensity for apredetermined period of time, the combination with an X-ray tube, ofmeans for supplying direct current to said X-ray tube including a valvetube having a thermionic cathode and a transformer for supplying heatingcurrent to said cathode, a time switch electrically associated with saidtransformer and operable for predetermined periods of time to causedirect current to flow to said X-ray tube, and means connected to saidtransformer and operable by said time switch for varying the heatingcurrent supplied to said cathode.

4. In an X-ray system for varying the intensity of the X-rays emanatingfrom an X-ray tube during a predetermined period of time, thecombination with an X-ray tube, of a source of electrical energy forsaid X-ray tube including means for rectifying the current supplied tosaid X-ray tube, means electrically associated with said rectifyingmeans and operable for predetermined periods of time to cause therectified current to be supplied to said X-ray tube, and means operableby said last mentioned means for automatically varying the amount ofcurrent supplied to said X-ray tube whereby the intensity of X-raysemanating from said tube will be varied during the time of operation ofsaid X-ray tube.

5. In an X-ray system for varying the intensity of the X-rays emanatingfrom an X-ray tube for a predetermined period of time, the combinationwith an X-ray tube, of a source of electrical energy therefor comprisinga rectifier tube having a thermionic cathode, means for heating saidcathode including a time switch operable to cause said means to heat thecathode of said rectifier tube for a predetermined period of time andrender said source effective to energize said X-ray tube, and meanselectrically associated with said means for heating said cathode andoperable by said time switch to vary the heating current supplied tosaid cathode whereby the current supplied to said X-ray tube is variedto produce X- rays of varying intensity during the period of operationthereof.

6. In an X-ray system for varying the intensity of the X-rays emanatingfrom an X-ray tube for a predetermined period of time, the combinationwith an X-ray tube of a source of high potential electrical energy forenergizing said X-ray tube, a valve tube connected to said X-ray tubeand to said source and operable to control the flow of current from saidsource to said X-ray tube, means electrically connected with said sourceand operable to cause said source to energize said X-ray tube for apredetermined period of time, and means electrically associated withsaid valve tube operable to vary the current flowing through the latterand consequently through said X-ray tube to thereby vary the intensityof the X-rays emanating therefrom,ysaid last mentioned means beingoperable by said rst mentioned means.

'7. In an X-ray system for varying the intensity of the X-rays emanatingfrom an X-ray tube for a predetermined period of time, the combinationwith an X-ray tube, of a source of high potential electrical energy forenergizing said X-ray tube, a valve tube connected with said source andsaid X-ray tube and operable to control the flow of current from saidsource to said X-ray tube, a time switch electrically associated withsaid source and operable to cause said source to energize said X-raytube for a predetermined period of time, and a rheostat electricallyassociated with said valve tube and operable by said time switch forvarying the current flowing through said valve tube and consequentlyAthrough said X-ray tube to cause a variation in the intensity of theX-rays emanating from said X-ray tube.

8. In an X-ray system for varying the X-ray intensity for apredetermined period of time, comprising the combination with an X-raytube, of a high tension transformer having a primary and secondarywinding, said secondary winding being connected to said X-ray tube,means for making and breaking a connection to said primary winding, avalve tube having a thermionic cathode connected in series with saidsecondary winding and said X-ray tube, a heating transformer for saidcathode, and means operable by said make and break means and connectedto said heating transformer for varying the flow of current in saidheating transformer.

9. In an X-ray system for varying the intensity of the X-rays emanatingfrom an X-ray tube for a predetermined period of time, the combinationwith an X-ray tube, of means for energizing said X-ray tube comprising asource of high potential electrical energy, a valve tube having' acathode to be heated connected to said source and said X-ray tube andoperable to control the flow of current from said source to said X-raytube, a source of heating current for the cathode of said valve tube,means operable to cause the cathode of said valve tube to be energizedby said source of heating current for a predetermined period of time andrender said valve tube operative to cause said 'high potential source toenergize said X-ray tube, and means electrically associated with saidsource of heating current for the cathode of said valve tube operable tovary the current flowing through said valve tube and consequentlythrough said X-ray tube and engageable by said second mentioned meansfor actuation thereby.

10. In an X-ray system for varying the intensity of the X-rays emanatingfrom an X-ray tube for a predetermined period of time, the combinationwith an X-ray tube of a high tension transformer for energizing saidX-ray tube and adapted to be connected to a source of electrical energy,a valve tube provided with a cathode to be heated associated with saidX-ray tube and said high tension transformer to cause electrical currentof one sign only to flow through said X- ray tube, a low tensiontransformer for supplying heating current to the cathode o f said valvetube and adapted to be connected to a source of electrical energy, meansassociated with said high tension transformer and said low tensiontransformer for connecting both said transformers to a source ofelectrical energy for a predetermined period of time, and meansassociated with said low tension transformer and said valve tube andoperable by said rst mentioned means to vary the current flowing throughsaid valve tube.

11. In an X-ray system for varying the intensity of the X-rays emanatingfrom an X-ray tube for a predetermined period of time, the combinationwith an X-ray tube of a high tension transformer 10 for energizing saidX-ray tube and adapted to be connected to a source of electrical energy,a valve tube provided with a cathode to be heated connected to saidX-ray tube and said high tension transformer to cause electrical currentof one sign only to flow through said X-ray tube, a. low tensiontransformer for supplying heating current to the cathode of said valvetube and adapted to be connected to a source of electrical energy, atime switch associated with said high tension and low tensiontransformers for connecting both said transformers to a source ofelectrical energy for a predetermined period of time, and a rheostatelectrically connected with said low tension transformer and the cathodeof said valve tube and operable by said time switch for varying thecurrent flowing through said valve tube and consequently through saidX-ray tube to cause X-rays of varying intensity to emanate from thelatter.

12. In an X-ray system for varying the intensity of the X-rays emanatingfrom an X-ray tube for a predetermined period of time, the combinationwith an X-ray tube of a high tension transformer for energizing saidX-ray tube provided with a primary and secondary winding, a valve tubeprovided with a cathode to be heated and connected in series with thesecondary winding of said high tension transformer and said X-ray tubeto cause electrical current of one sign only to flow through said X-raytube, a low tension transformer provided with primary and secondarywindings for supplying heating currents to the cathode of said valvetube, a time switch associated with the primary winding of said hightension and low tension transformers and operable to connect the same toa source of electrical energy for a predetermined period of time, and arheostat connected in series with the primary winding of said lowtension transformer and operable by said time switch to cause avariation in the current flowing through said valve and X-ray tubes toproduce a variation in the intensity of the X-rays emanating from saidX-ray tube.

MONTFORD MORRISON.

